historywikiaorg-20200223-history
Clock face
A clock face is the part of an analog clock that tells time through the use of a fixed numbered dial or dials and moving hand or hands. Typically, the dial is numbered 1-12 indicating the hours in a 12-hour cycle. The term face is also used for the time display on digital clocks and watches. Certain clocks have 24-hour analog displays and are marked accordingly. Some special purpose clocks, such darkroom timers and sporting event clocks, are designed for measuring periods less than one hour. Clocks can indicate the hour with Roman numerals or Hindu-Arabic numerals. The two numbering systems have also been used in combination with the prior indicating the hour and the later the minute. Longcase clocks (also known as grandfather clocks) typically use Roman numerals for the hours. ("IIII" -rather than "IV"- is often used to mark the fourth hour to achieve symmetry with "VIII.") Clocks using only Arabic numerals first began to appear in the mid-18th century. In some instances, particularly in the case of watches, the numbers are replaced with undifferentiated hour markings. Occasionally markings of any sort are dispensed with. The face of the Movado "Museum Watch" is known for a single dot at the 12 o'clock position. Historical and stylistic development Clocks existed before clock faces. The original clocks were striking clocks: their purpose was to ring bells upon the passage of a certain amount of time. These clocks were erected as tower clocks in public places, to ensure that the bells were audible; their purpose was to mechanize and eliminate the human element from the ringing of bells as a public time signal. It was not until these mechanical clocks were in place that their creators determined that their wheels could be used to drive an indicator on a dial. The first weight-driven mechanical clocks, employing a mercury escapement mechanism and a clock face similar to an astrolabe dial, were also invented by Muslim engineers in the 11th century. A similar weight-driven mechanical clock later appeared in a Spanish language work compiled from earlier Arabic sources for Alfonso X in 1277.Ahmad Y Hassan, Transfer Of Islamic Technology To The West, Part II: Transmission Of Islamic Engineering, History of Science and Technology in Islam. The knowledge of weight-driven mechanical clocks produced by Muslim engineers in Spain was transmitted to other parts of Europe through Latin translations of Arabic and Spanish texts on Muslim mechanical technology. In the early 11th century, Ibn al-Haytham's Maqala fi al-Binkam described a mechanical water clock that, for the first time in history, accurately measures time in hours and minutes. To represent the hours and minutes, Ibn al-Haytham invented a clock face. It featured a 24-hour analog dial, including a large marker for each hour and a small marker for each minute, along with medium-sized markers to indicate half-hours and quarter-hours.Salim Al-Hassani, The Mechanical Water Clock Of Ibn Al-Haytham, Muslim Heritage Before the late 15th century, a fixed hand indicated the hour by pointing to rotating numbers (in contrast with the modern system of a fixed dial and rotating hands). In the Ottoman Empire, Taqi al-Din invented the "observational clock", which he described as "a mechanical clock with three dials which show the hours, the minutes, and the seconds." This was the first clock to measure time in seconds, and was used for astronomical purposes, specifically for measuring the right ascension of the stars. This is considered one of the most important innovations in 16th century practical astronomy, as previous clocks were not accurate enough to be used for astronomical purposes.Sevim Tekeli, "Taqi al-Din", in Helaine Selin (1997), Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures, Kluwer Academic Publishers, ISBN 0-7923-4066-3. At the Istanbul observatory of Taqi al-Din, he further improved his observational clock, using only one dial to represent the hours, minutes and seconds, describing it as "a mechanical clock with a dial showing the hours, minutes and seconds and we divided every minute into five seconds." (cf. ) In Christian Europe, minute hands only came into use in the late 17th century after the invention of the pendulum allowed for increased precision in time telling. Until the last quarter of the 17th century hour markings were etched into metal faces and the recesses filled with black wax. Subsequently, higher contrast and improved readability was achieved with white enamel plaques painted with black numbers. Initially, the numbers were printed on small, individual plaques mounted on a brass substructure. This was not a stylistic decision, rather enamel production technology had not yet achieved the ability to create large pieces of enamel. The "13 piece face" was an early attempt to create an entirely white enamel face. As the name suggests, it was composed of 13 enamel plaques: 12 numbered wedges fitted around a circle. The first single piece enamel faces, not unlike those in production today, began to appear c. 1735. References Category:Clocks